Detection apparatus and method

1. A transceiver apparatus comprising:

first means for detecting over a first detection period and providing a first output indicating a beginning of a message with first detection probability,

second means for detecting over a second detection period being greater than the first detection period and providing a second output indicating the detection of the beginning of the message with a second detection probability, and said second detection period is shorter than the time from the beginning of the message to the time where reception of the message must be started in order to successfully receive the message,

wherein said second detection probability is higher than said first detection probability, and

said transceiver apparatus is arranged to receive the message if said second means for detecting indicates detection of the beginning of the message.

2. The transceiver apparatus according to claim 1 , wherein

said transceiver is arranged to transmit a message if said first means for detecting does not indicate a beginning of a message.

3. The transceiver apparatus according to claim 2 , wherein

said transceiver is arranged to transmit a message depending on a plurality of additional parameters.

4. The transceiver apparatus according to claim 3 , wherein

a parameter indicates if a message is available for sending or if the transceiver apparatus is allowed to transmit.

5. The transceiver apparatus according to claim 1 , wherein

said first and second detection periods have the same start time.

6. The transceiver apparatus according to claim 1 , wherein

said first means for detecting is optimized to minimize the probability of falsely indicating a message beginning while meeting minimum detection requirements.

7. The transceiver apparatus according to claim 1 , wherein

said second means for detecting is optimized to maximize the probability of detection of a message beginning while meeting required maximum rates of false positive indications.

8. The transceiver apparatus according to claim 1 , arranged to receive and transmit messages over a medium, wherein

said first and second means for detecting are arranged to start detecting at the start of a defined time-slot,

said first means for detecting is arranged to indicate the presence or absence of a message on said medium after a first CCA time,

said second means for detecting is arranged to indicate the presence or absence of a message on said medium after a second CCA time,

said second CCA time is substantially longer than said first CCA time,

if said first means for detecting indicates the absence of a message on said medium, said transceiver is arranged to evaluate if said transceiver is allowed to send a message, and if said evaluation is positive, start sending a message in the next time-slot,

if said first means for detecting indicates the presence of a message on said medium after said first CCA time, and said second means for detecting indicates the presence of a message on said medium after said second CCA time, said transceiver is arranged to receive and decode said message present on said medium, and

if said first means for detecting indicates the presence of a message on said medium after said first CCA time, and if said second means for detecting indicates the absence of a message on said medium, after said second CCA time, said transceiver is arranged to start detecting the presence or absence of a message at the start of the next available time-slot.

9. A method for detecting the beginning of a message in a transceiver apparatus comprising a detector and a decoder, comprising the steps of:

detecting, using a first set of detection parameters and a first detection process, the beginning of an incoming message for a first time period,

detecting, using a second set of detection parameters and a second detection process, the beginning of said incoming message for a second time period, the second time period being greater than the first time period and the second time period is shorter than the time from the beginning of said incoming message to the time where reception of said incoming message must be started in order to successfully receive said incoming message and

decoding said incoming message if said detection during said second time period indicates the presence of said incoming message.

10. The method according to claim 9 , wherein said transceiver apparatus further comprises a transmitter and the further step of:

starting transmission of a message if a message is ready for transmission and if said detection during said first time period indicates that no message is received.

11. The method according to claim 9 , wherein

said first and second detection process start detecting incoming messages simultaneously.

12. The method according to claim 10 , wherein

said first and second detection process start detecting incoming messages simultaneously.

13. A transceiver apparatus comprising:

a first detector arranged to operate over a first detection period, wherein the output from said first detector indicates the beginning of a message with a first detection probability,

a second detector arranged to operate over a second detection period being greater than said first detection period and said second detection period is shorter than the time from the beginning of the message to the time where reception of the message must be started in order to successfully receive the message, wherein the output from said second detector indicates the detection of the beginning of the message with a second detection probability,

said second detection probability is higher than said first detection probability, and wherein

said transceiver apparatus is arranged to receive said message if said second detector indicates detection of the beginning of the message.

14. The transceiver apparatus according to claim 13 , wherein

said transceiver is arranged to transmit a message if said first detector does not indicate a beginning of a message.

15. The transceiver apparatus according to claim 14 , wherein

said transceiver is arranged to transmit a message depending on a plurality of additional parameters.

16. The transceiver apparatus according to claim 13 , wherein

said first and second detection periods have the same start time.

17. The transceiver apparatus according to claim 13 , wherein

said first detector is optimized to minimize the probability of falsely indicating a message beginning while meeting minimum detection requirements.